Mosul is Iraq's second largest city and the ISIS group's last major urban bastion in the country

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Kurdish security forces take up a position as they fight overlooking the Islamic State-controlled in villages surrounding Mosul, in Khazer, about 30 kilometers (19 miles) east of Mosul, Iraq, Monday, Oct. 17, 2016. Iraqi government and Kurdish forces, backed by U.S.-led coalition air and ground support, launched coordinated military operations early on Monday as the long-awaited fight to wrest the northern city of Mosul from Islamic State fighters got underway.

Iraqi and Kurdish commanders said Tuesday they have paused their advance on Mosul a day after the start of a massive operation to retake the Islamic State-held city, which is expected to take weeks, if not months.

The front lines to the east of Mosul were largely quiet, a day after Iraqi Kurdish forces advanced amid a barrage of U.S.-led airstrikes and heavy artillery.

"We are just holding our positions," said Col. Khathar Sheikhan, of the Kurdish forces known as the peshmerga, which captured a handful of villages east of Mosul on Monday. "The Iraqi army will now advance past our arenas of control."

But an Iraqi special forces commander said his troops have delayed an advance following a request from Kurdish forces for more time to achieve their goals. It was not immediately possible to reconcile the conflicting accounts.

Brig. Gen. Haider Fadhil said his men had planned to move at dawn, but postponed the operation. He said Iraqi army and Kurdish commanders would meet later on Tuesday.

Iraqi Prime Minister Haider al-Abadi had announced the long-awaited offensive before dawn Monday, vowing to liberate the city from more than two years of extremist rule. Mosul is Iraq's second largest city and the IS group's last major urban bastion in the country.

The large and complex battle for Mosul is expected to last weeks or months. It will involve more than 25,000 troops, including the Iraqi army, the Kurdish peshmerga, Sunni tribal fighters and Shiite militias. The U.S. military is providing air support and playing a supporting role on the ground.

A spokesman for the U.S.-led coalition said the operation was proceeding as planned and that Iraqi forces were making "excellent progress."

"There's no pause in efforts to liberate Mosul. Troops are on the move on various axes of advance toward the city," said Col. John Dorrian. "Some commanders have reached their objectives ahead of schedule after encountering light-to-moderate resistance."

By the end of the day Monday, Kurdish forces had retaken some 200 square kilometers (80 square miles), according to Massoud Barzani, the president of Iraq's largely autonomous Kurdish region.

Peshmerga commanders on the ground estimated they retook nine villages and pushed the front line with IS back eight kilometers (five miles). The front line east of Mosul is now some 30 kilometers (20 miles) from the city.

IS said it carried out 12 suicide attacks on Monday against the forces advancing on Mosul, including eight that targeted the peshmerga. The report carried by the IS-run Aamaq news agency said Iraqi forces had captured just three villages and that IS fighters had halted an advance from the south.